I'm not convinced that's the best way to measure it, as how far the steerer goes into the headtube may be affected by the shape of the fork crown.
Measure the length of the head tube and add the stack height of the headset of your choice. This tells you how much steerer you need.
Now measure your steerer and discover if you have enough steerer and/or how much you'll need in the way of spacers.
I'm not convinced that's the best way to measure it, as how far the steerer goes into the headtube may be affected by the shape of the fork crown.
Measure the length of the head tube and add the stack height of the headset of your choice. This tells you how much steerer you need.
Now measure your steerer and discover if you have enough steerer and/or how much you'll need in the way of spacers.